<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        ul{
            display: none;
        }
        button {
            display: block;
        }
    </style>
</head>
<body>

    <div class="c">
        <button>111</button>
        <ul>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
        </ul>
        <button>111</button>
        <ul>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
        </ul>
        <button>111</button>
        <ul>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
        </ul>
        <button>111</button>
        <ul>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
            <li>11111</li>
        </ul>
    </div>

    <script src="../js/jq.js"></script>
    <script>

        $('button').on('click' , function() {
            console.log(this);  // button
            $(this).next().slideToggle(300,() => {
                console.log(6);
            })
        })

    </script>
    
</body>
</html>